This invention relates to a method and a device for manufacturing bearing blanks, and more particularly for forming two blanks (for outer and inner bearing rings) from a single material.
FIG. 8 shows a conventional method for forming bearing blanks to be formed into outer and inner rings of a bearing from a single material. This method (consists of the following five steps.
First Step: A columnar piece B0 shown in FIG. 8A is hot swaged axially to form a disk-shaped piece B1 having an arcuate outer periphery 101 as shown in FIG. 8B.
Second Step: The disk-shaped piece B1 is formed into a stepped cylindrical piece B2 shown in FIG. 8C by die forging. The piece B2 comprises an outer cylindrical portion 102 and an inner cylindrical portion 103 having its top end integrally joined to the inner surface of the outer cylindrical portion 102. The inner cylindrical portion 103 has an inner bottom 104.
Third Step: The outer cylindrical portion 102 and the inner cylindrical portion 103 having the bottom are separated from each other as shown in FIG. 8D by shearing the cylindrical piece B2 axially along the chain line of FIG. 8C.
Fourth Step: The bottom 104 of the inner cylindrical portion 103 is removed by a punch to form a blank 106 for an inner bearing ring (FIG. 8E).
Fifth Step: The outer cylindrical portion 102 is subjected to rolling to increase its diameter and form an annular groove in the inner surface, thus forming a blank 107 for an outer bearing ring shown in FIG. 8F.
The first to fourth steps are hot processes continuously carried out by a forging machine. Then, the outer cylindrical portion 102 and the inner cylindrical portion 103 are taken out of the forging machine. The fifth step, a diameter-increasing step, is carried out in the cold by a roll former shown in FIG. 9.
The roll former comprises main rollers 110 each having a groove and a mandrel 111 having an annular rib 112. By rotating the main rollers 110 with the outer cylindrical portion 102 pressed against one of the main rollers 110 by the mandrel 111, the cylindrical portion is diametrically expanded gradually. At the same time, an annular groove 108 is formed in the inner periphery thereof.
The outer cylindrical portion 102 has a shoulder 105 formed on its inner periphery. The shoulder 105 is inevitably formed when the cylindrical piece B2 is separated axially into the outer and inner portions in the third step. Thus, if the outer cylindrical portion 102 has no shoulder on its outer periphery, this means that there is a difference in thickness at both ends of the outer cylindrical portion 102. Such a difference in thickness at both ends will make it difficult to form an intended blank 107 for an outer bearing ring by rolling.
In order to avoid such a difference in thickness at both ends and to form a high-quality outer ring blank by rolling, it is necessary to form a shoulder 109 on the outer periphery of the outer cylindrical portion during die forging in the second step.
The blank 106 for an inner bearing ring formed in the fourth step, and the blank 107 for an outer bearing ring formed in the fourth step are formed into an inner ring 7b and an outer ring 7a of a ball bearing 7 shown in FIG. 10 by lathing, cutting, heat treatment, etc.
In the conventional method of manufacturing bearing ring blanks shown in FIG. 8, in addition to the multistage feed type forging machine for carrying out the first to fourth steps, a roll former for cold roll forming in the fifth step is separately needed. Therefore, the facility cost tends to be high.
Further, the step of separating the cylindrical piece B2 into the outer cylindrical portion 102 and the inner cylindrical portion 103 having the bottom (Third Step) and the step of punching the bottom 104 from the inner cylindrical portion 103 (Fourth Step) are separate steps. Thus, a large number of steps are needed to manufacture an outer bearing ring blank. Also, since the roll forming in the fifth step is carried out in the cold, productivity is low.
An object of this invention is to provide a separating/punching method and device which can improve productivity of bearing blanks and which makes it possible to manufacture blanks for inner and outer bearing rings with a single multistage forging machine.